1. Technical Field
The present invention relates to a liquid ejection apparatus such as an inkjet type printer.
2. Related Art
Typically, an inkjet type printer (hereinafter, referred to as a printer) is broadly known as a liquid ejection apparatus that ejects liquid onto a target. In the printer, ink (the liquid) is supplied from an ink cartridge retaining the ink to a recording head (a liquid ejection head), which ejects the ink. The recording head ejects the ink through a nozzle defined in a nozzle forming surface of the recording head onto a sheet of recording paper, or the target, thus subjecting the sheet of paper to printing. If the ink cartridge is arranged at a position spaced from the recording head, as in some printers, the ink is supplied from the ink cartridge to the recording head through a tube routed in the printer.
To change the ink to be ejected from the nozzle of the recording head to a different type of ink, supply of the ink from the currently used ink cartridge to the recording head is suspended. In this state, the ink is drained from the tube through the nozzle of the recording head. The different type of ink is then supplied from a corresponding ink cartridge, which retains this type of ink, to the recording head through the tube.
However, such drainage of the ink in switching of the types of the ink wastefully increases consumption of the ink. To solve this problem, Japanese Laid-Open Patent Publication No. 2006-175626 proposes a printer having a switching device that is connected to tubes extending from respective ink cartridges and arranged in the vicinity of a recording head.
In the printer of Japanese Laid-Open Patent Publication No. 2006-175626, the types of ink supplied to the recording head is switched between a first type of ink (first liquid) and a second type of ink (second liquid) in the switching device. Specifically, in the switching device, the downstream end of a first passage (a first supply passage) that supplies the first type of ink and the downstream end of a second passage (a second supply passage) that supplies the second type of ink are joined together. A head supply passage through which the ink is supplied to the recording head is provided between the joining point and the recording head. The switching device accommodates a first diaphragm (a first ON-OFF valve), which selectively opens and closes the first passage, and a second diaphragm (a second ON-OFF valve), which selectively opens and closes the second passage. Supply of the ink is thus switched between the first type of ink and the second type of ink by closing one of the diaphragms and opening the other.
To supply the first type of ink to the recording head, the switching device opens the first diaphragm and closes the second diaphragm. Contrastingly, to supply the second type of ink to the recording head, the switching device opens the second diaphragm and closes the first diaphragm.
When the first diaphragm is open and the second diaphragm is closed in the above-described printer, the portion of the second passage between the joining point of the first and second passages and the second diaphragm forms a “dead end” portion. Similarly, when the second diaphragm is open and the first diaphragm is closed in the printer, the portion of the second passage between the joining point of the first and second passages and the first diaphragm forms a “dead end” portion.
Thus, when the first type of ink is supplied to the recording head, some of the ink is led from the first passage into the dead end portion of the second passage via the joining point and retained in the dead end portion. When the second type of ink is supplied to the recording head, some of the ink is sent from the second passage into the dead end portion of the first passage via the joining point and retained in the dead end portion.
The properties of the ink retained in the dead end portions deteriorate as the time elapses and the ink with the deteriorated properties gradually diffuses from the dead end portion and flows into the head supply passage. This adversely influences the properties of the ink to be ejected from the nozzle of the recording head.